The present invention generally relates to rotation quantity measuring methods and systems, and more particularly to a rotation quantity measuring method and system for measuring a rotation quantity of an arbitrary rotary body which is applicable to various rotary encoders.
As a method of measuring a rotation quantity of an object body, there is a conventional method which forms a grating pattern on a peripheral portion of a disc shaped rotary body as an encoder pattern and fixes the rotary body on the object body so that the rotary body rotates integrally with the object body. According to this conventional method, the rotation quantity of the object body is measured by optically detecting a movement of the encoder pattern. For example, "The Use of Optical Parts and Consideration to be Given", Optronics Company, 1985 proposes this conventional method.
However, the above described conventional method suffers from the following problems. First, a measuring apparatus which employs the conventional method becomes bulky because the rotary body which is fixed on the object body has a disc shape. Second, the patterning of the grating pattern on the rotary body is formed by a photolithography, but it is troublesome to carry out a large number of patterning steps which are required to form the grating pattern. Third, when setting a pitch of gratings of the grating pattern to one micron or less so as to obtain a high resolution, for example, the patterning must be carried out over a large area thereby making it difficult to improve the accuracy of the measurement.
Therefore, there is a demand to realize a rotation quantity measuring method which does not require a bulky measuring apparatus and which is capable of making a highly accurate measurement.